1-Go to you Blog Themes
2-Click Layout
3-Copy below code paste to Add a Gadget

Youtube Id Channel ( UCXlDtm7S3Wjr6vytUMcKu6A )
Style 1 (Normal)

<script src="https://apis.google.com/js/platform.js"></script>
<div class="g-ytsubscribe" data-channelid="UCXlDtm7S3Wjr6vytUMcKu6A" data-layout="full" data-count="default"></div>

Youtube Id Channel ( UCXlDtm7S3Wjr6vytUMcKu6A )
Style 2 (Dark Background)

<script src="https://apis.google.com/js/platform.js"></script>
<div class="g-ytsubscribe" data-channelid="UCXlDtm7S3Wjr6vytUMcKu6A" data-layout="full" data-theme="dark" data-count="default"></div>

Youtube Id Channel ( XlDtm7S3Wjr6vytUMcKu6A )
Style 3 (Wiht Iframe)

<iframe src="http://www.youtube.com/subscribe_widget?p=XlDtm7S3Wjr6vytUMcKu6A" style="overflow: hidden; height: 72px; width:100%" scrolling="no" frameborder="0">
    </iframe>

4-Save Your Template is OK

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